This invention relates generally to semiconductor packaging. More particularly, this invention relates to a stackable semiconductor package having an internal conductive layer, to a method for fabricating the package and to an electronic assembly incorporating the package.
Semiconductor dice or chips are typically contained in semiconductor packages. This is sometimes referred to as the first level of packaging. A package is required to support, protect, and dissipate heat from a die, and to provide a lead system for power and signal distribution to the die. Typically, the package includes a substrate for supporting the die, an encapsulant for protecting the die and external contacts that provide the lead system to the die.
For example, the substrate can comprise a lead frame for plastic packages, or a circuit board material for BGA packages. The encapsulant can comprise a plastic body which completely encloses the die and the substrate, or simply a glob top which encapsulates only the die. Depending on the type of package, the external contacts can comprise leads, solder balls, pads or pins.
Semiconductor packages can also be constructed such that several packages can be stacked with their external contacts electrically interconnected. The present invention is directed to a semiconductor package that is designed for stacking with similar packages for constructing an electronic assembly. The package includes an internal conductive layer that simplifies the fabrication process, and allows different packages of the assembly to have different circuit configurations.
In accordance with the present invention, a stackable semiconductor package, a method for fabricating the package, and an electronic assembly constructed using multiple packages are provided.
The package includes a substrate, and a semiconductor die attached to the substrate. The substrate comprises three separate layers including a conductive layer having conductive traces in a desired configuration, and first and second insulating layers on opposing sides of the conductive layer. One of the insulating layers covers the die, and one of the insulating layers covers the conductive traces. The package also includes electrically conductive vias through the insulating layers in electrical communication with the conductive traces. In addition, the package includes arrays of external contacts, such as pads or balls, arranged in matching patterns on each insulating layer in electrical communication with the conductive vias and the conductive traces.
In a first embodiment of the package, the conductive layer comprises a segment of a lead frame having lead fingers which form the conductive traces. In addition, the die is attached and wire bonded to the lead fingers, and the insulating layers are applied to the opposing sides of the lead fingers. Further, the insulating layers comprise a polymer, such as a photoimageable resist, a cured layer, or a tape material, that is etched, developed or machined with openings for the conductive vias.
In a second embodiment of the package, the conductive layer comprises a metal layer, such as copper, patterned with the conductive traces. In this embodiment, the metal layer can be deposited on, or laminated to one of the insulating layers, and then etched to form the conductive traces. In addition, the die is flip chip mounted to the conductive traces, and covered by the other insulating layer.
A method for fabricating the first embodiment package includes the steps of providing the lead frame, and then attaching and wire bonding a plurality of dice to the lead fingers. The method also includes the steps of forming the insulating layers on the lead fingers and the die, forming the openings in the insulating layers, and then depositing a conductive material into the openings to form the conductive vias. In addition, the method includes the steps of forming matching patterns of external contacts on the insulating layers in electrical communication with the conductive vias, and then singulating the lead frame into separate packages.
A method for fabricating the second embodiment package includes the steps of providing the conductive layer on the first insulating layer, and etching the conductive layer to form the conductive traces. In this embodiment the conductive layer and the first insulating layer can be provided as a bi-material panel, such as a glass resin/copper laminate. The method also includes the step of flip chip bonding a plurality of dice to the conductive traces, and then covering the dice with the second insulating layer. In addition, the method includes the steps of forming matching patterns of external contacts on the insulating layers in electrical communication with the conductive vias, and then singulating the panel into separate packages.
In either embodiment, the package is configured for stacking to substantially similar packages to form the electronic assembly. In addition, different packages of the assembly can have different configurations of conductive traces or wire bonds, that provide customized circuit configurations for the different layers of the assembly. This allows selected packages of the assembly to perform a required electronic function, such as address, while the remaining package perform other electronic functions. Rather than providing different circuit configurations in the conductive traces, different wire bonding configurations for the conductive traces can be used.